feat: compact notation for inspecting grind state

[leodemoura]

This PR implements a compact notation for inspecting the grind state in interactive mode. Within a grind tactic block, each tactic may optionally have a suffix of the form | filter?.

Examples:

instantiate | gen > 0  -- Displays terms in the `grind` state after executing `instantiate` with generation greater than zero

instantiate |  -- Displays the `grind` state after executing `instantiate`

Remark: If the user places the cursor one space before |, the state before executing instantiate is displayed.
This PR removes the code that was silently displaying the grind state after each tactic step, as it was too noisy.
It also updates the notation for the first combinator in the grind tactic mode to avoid conflicts with the new syntax.